A 39-year-old man came to us for surgical treatment of a hidradenitis suppurativa. Upon excision of a perianal abscess, the diagnosis of a rare tumor, a perianal mucinous adenocarcinoma (pT4, pN 1, MO), was made. An abdominoperineal resection was performed, followed by a combination of adjuvant radiation and chemotherapy. A year after the operation, the patient is doing well without any signs of recurrence. This carcinoma probably arises in the anal glands. It often presents as a perirectal abscess and/or an anal fistula. Therefore, the diagnosis is often delayed. At presentation, the tumor is bigger than 5 cm in diameter in 80% of the cases, and the prognosis is poor. It metastasizes mostly to the superficial inguinal or to the retrorectal lymph nodes. There are only case reports and no comparative studies in the literature. In the last 10 years, the carcinoma has mostly been treated by neoadjuvant radiation and chemotherapy, followed by abdominoperineal resection. Since then, the median survival has increased to 3 years. This is the first case report of a combination of a perianal mucinous adenocarcinoma with a hidradenitis suppurativa.